1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to an apparatus for quickly, accurately, and automatically cutting a sheet material of the type that can be used to define a mold element, such as a molding pad for producing cogged power transmission belts. The invention further contemplates a method of cutting a rubber sheet material using the inventive apparatus.
2. Background Art
Power transmission belts are known in which cogs are spaced at regular or irregular intervals along the length of the belt. These cogged belts, which are normally "raw edge" belts, may be formed by different processes, among which are the "preform" or "spancog" processes. In the conventional preformed process, a fabric layer and an unvulcanized rubber sheet are applied in turn against a mold that has alternating cogs and notches. The laminated sheet and fabric layers are pressed against the mold to conform thereto and define a cogged mold pad. The preformed cogged pad is then wrapped around a cylindrical core on a molding drum. The ends of the cogged pad are each cut in a straight line and abutted together to define an endless, cylindrical configuration around the core. A belt sleeve can then be formed by sequentially wrapping components around the pad.
To consistently define a high quality cogged pad, it is important to precisely precut the pad so that the ends thereof can be closely matched when butted. Typically, the cogged pad is spread out and marked to be cut to the appropriate length. An experienced operator will count the cogs and make a mark, as with chalk, on the cog to be cut. The operator then manually severs the pad with a cutter along the marked cog to define one butt end of the pad. The other pad end is defined in similar fashion.
Proper pad formation requires that the butt ends of the pad be cut so as not only to be straight in a transverse direction, but so that the end thicknesses precisely match when the ends are joined. If the matching is imprecise in terms of the straightness, thickness or angle of the butt edges, an inferior or incomplete joint may result between the butt ends. For example, if the pad is not cut precisely at the cog top, the edge thicknesses will not match. A gap may also form in a worse case, causing a volume crack and resulting in a failed joint. A belt made with the defective pad may develop a crack at the location of the joint as a result of load fluctuation or heat generation as the belt is running.